Commit 266991b1 authored by Jeff Moyer's avatar Jeff Moyer Committed by Theodore Ts'o
Browse files

ext4: fix race between unwritten extent conversion and truncate 



The following comment in ext4_end_io_dio caught my attention:

	/* XXX: probably should move into the real I/O completion handler */
        inode_dio_done(inode);

The truncate code takes i_mutex, then calls inode_dio_wait.  Because the
ext4 code path above will end up dropping the mutex before it is
reacquired by the worker thread that does the extent conversion, it
seems to me that the truncate can happen out of order.  Jan Kara
mentioned that this might result in error messages in the system logs,
but that should be the extent of the "damage."

The fix is pretty straight-forward: don't call inode_dio_done until the
extent conversion is complete.

Reviewed-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarJeff Moyer <jmoyer@redhat.com>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org
parent d4dc462f

fs/ext4/ext4.h

+1 −0
Original line number Diff line number Diff line
@@ -184,6 +184,7 @@ struct mpage_da_data { 
#define	EXT4_IO_END_UNWRITTEN	0x0001

#define EXT4_IO_END_ERROR	0x0002

#define EXT4_IO_END_QUEUED	0x0004

#define EXT4_IO_END_DIRECT	0x0008



struct ext4_io_page {

	struct page	*p_page;

fs/ext4/inode.c

+5 −5
Original line number Diff line number Diff line
@@ -2796,9 +2796,6 @@ out: 


	/* queue the work to convert unwritten extents to written */

	queue_work(wq, &io_end->work);



	/* XXX: probably should move into the real I/O completion handler */

	inode_dio_done(inode);

}



static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate)
@@ -2922,9 +2919,12 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb, 
		iocb->private = NULL;

		EXT4_I(inode)->cur_aio_dio = NULL;

		if (!is_sync_kiocb(iocb)) {

			iocb->private = ext4_init_io_end(inode, GFP_NOFS);

			if (!iocb->private)

			ext4_io_end_t *io_end =

				ext4_init_io_end(inode, GFP_NOFS);

			if (!io_end)

				return -ENOMEM;

			io_end->flag |= EXT4_IO_END_DIRECT;

			iocb->private = io_end;

			/*

			 * we save the io structure for current async

			 * direct IO, so that later ext4_map_blocks()

fs/ext4/page-io.c

+2 −0
Original line number Diff line number Diff line
@@ -110,6 +110,8 @@ int ext4_end_io_nolock(ext4_io_end_t *io) 
	if (io->iocb)

		aio_complete(io->iocb, io->result, 0);



	if (io->flag & EXT4_IO_END_DIRECT)

		inode_dio_done(inode);

	/* Wake up anyone waiting on unwritten extent conversion */

	if (atomic_dec_and_test(&EXT4_I(inode)->i_aiodio_unwritten))

		wake_up_all(ext4_ioend_wq(io->inode));

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